Update Slack member count (hackclub#1377)

We're at 10K now :)

README.md

@@ -6,7 +6,7 @@
 
 We think learning to code is uniquely like gaining a superpower: it converts you from a _consumer_ to a _creator_, turning your computer into a tool for creation. If you’re reading this, you can learn to build an app—there’s never been a better time for making.
 
-**The goal of Hack Club is to help you become a hacker.** We want an inclusive space on the internet & at every school where people are making interesting things with code, every week. In our [online Slack](https://slack.hackclub.com) (Discord-style online chatroom with 9K student members), you can ask coding questions, you’ll meet amazing friends, share projects you’re building, and so much more. Most members start with little to no coding experience, join our Slack, build projects of their own, [start clubs](https://hackclub.com/clubs/) at their school, attend & later organize [hackathons](https://hackathons.hackclub.com).
+**The goal of Hack Club is to help you become a hacker.** We want an inclusive space on the internet & at every school where people are making interesting things with code, every week. In our [online Slack](https://slack.hackclub.com) (Discord-style online chatroom with 10K student members), you can ask coding questions, you’ll meet amazing friends, share projects you’re building, and so much more. Most members start with little to no coding experience, join our Slack, build projects of their own, [start clubs](https://hackclub.com/clubs/) at their school, attend & later organize [hackathons](https://hackathons.hackclub.com).
 
 Hack Club was founded by [a teenager](https://zachlatta.com) who dropped out of high school because the school system wasn’t working. We’re an entirely open source organization—[our website](https://github.com/hackclub/v3) to even [our finances](https://bank.hackclub.com/hq) are public. It’s backed by everyone from [Elon Musk](https://hackclub.com/elon/) to GitHub co-founder Tom Preston-Werner.